ErrFutureBlock is returned when a block's timestamp is in the future according to the current node.

ErrInvalidNumber is returned if a block's number doesn't equal it's parent's plus one.

ErrPrunedAncestor is returned when validating a block requires an ancestor that is known, but the state of which is not available.

ErrUnknownAncestor is returned when validating a block requires an ancestor that is unknown.

ChainReader defines a small collection of methods needed to access the local blockchain during header verification.

Engine is an algorithm agnostic consensus engine.